White light emitting diodes including a nitride semiconductor are used widely as a light source for backlight of small liquid crystal display such as cellular phone, and an application as a light source is expected instead of fluorescent lamps from now on. For replacing fluorescent lamps with white light emitting diodes, cost saving is an important problem together with improvement in luminous efficiency. Furthermore, in new technology such as micro machine and capsule type gastric camera, demand for micro lighting is expected to rapidly grow in the future.
White light emitting devices and white light emitting diodes including a nitride semiconductor often used recently are produced, for example, by the following process. First, an epitaxial wafer is subjected to processing such as etching and electrode evaporating coating under suitable conditions, then, one or a plurality of diode chips cut from the wafer by dicing are fixed to a package in the form of cup, and bonding is carried out. Thereafter, a phosphor layer is formed, encapsulated with high transparent resin such as an epoxy resin or silicone resin, and the resin is formed in the form of lens to obtain light emitting diodes. For formation of a phosphor layer, there is generally used a method in which a phosphor is mixed with an epoxy resin or silicone resin, and the mixture is coated quantitatively using a highly accurate, repeatable dispenser. By placing a suitable number of the white light emitting diodes on a substrate for mounting, a white light emitting device having necessary brightness is produced.
White emission lighting including light emitting diodes are classified into two types from the standpoint of structure. In one type, white color is provided by combining a blue light emitting diode with a yellow fluorescent material. In another type, white color is provided by mixing light emissions from three light emitting diodes which emit respectively light three primary colors.
The conventional method of producing white light emitting devices and white light emitting diodes including a nitride semiconductor is as described above, thus, the method is complicated, a special production apparatus is required for maintaining assembly accuracy and quantification precision in the steps of the method, and additionally, checks for every steps are also necessary, leading to a necessity of large equipment investment generating correspondent production cost.
In the case of a white light emitting device used for a light source of backlight or lighting, there are a method in which white color is provided by combination of a blue light emitting diode and a yellow phosphor as described above, and a method in which white color is provided by mixing light emissions from light emitting diodes emitting respectively red (R), green (G) and blue (B), as shown in FIG. 16. The latter is excellent in color rendering as compared with the former, however, if light emission intensity in any one of the three color light emitting diodes changes, color tone, namely its light emitting spectrum pattern tends to vary.
On the other hand, among various lightings marketed widely, a lighting showing various color tones depending on its light emitting device property is provided. there are various color tones such as bulb color, daylight color. These are used property depending on the use object, preference of a user, and the like under various use environments. However, when the use object varies at the same use place or when lighting of different color tone is required by replacement of a user, change of preference of a user itself and the like, it becomes necessary to change the kind of a lighting or to control at most its intensity (brightness), leading to a requirement for a light emitting device capable of controlling color tone more simply and more easily and a lighting including this device.
In the conventional technology, it is necessary to arrange light emitting diode chips by handling them one by one as shown in FIG. 16, in producing a white light emitting device including a light emitting diode. However, since the light emitting diode device has small chip size, handling thereof is difficult. As a result, an expensive high precision handling machines is required, and additionally, it is difficult to scale down the chip size of the light emitting diode device at our disposal, thus, cost saving is difficult.